From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932355Ab1IHIWl (ORCPT ); Thu, 8 Sep 2011 04:22:41 -0400 Received: from 173-166-109-252-newengland.hfc.comcastbusiness.net ([173.166.109.252]:58411 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932322Ab1IHIWj (ORCPT ); Thu, 8 Sep 2011 04:22:39 -0400 Date: Thu, 8 Sep 2011 04:22:29 -0400 From: Christoph Hellwig To: Vivek Goyal Cc: Christoph Hellwig , Konrad Rzeszutek Wilk , Jeremy Fitzhardinge , jbeulich@novell.com, linux-kernel@vger.kernel.org, JBeulich@suse.com Subject: Re: Help with implementing some form of barriers in 3.0 kernels. Message-ID: <20110908082229.GB14549@infradead.org> References: <20110907174832.GN32190@dumpdata.com> <20110907181740.GG31726@redhat.com> <20110907201620.GB26548@infradead.org> <20110907213137.GJ31726@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110907213137.GJ31726@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 07, 2011 at 05:31:37PM -0400, Vivek Goyal wrote: > I have a basic question. In old guest why BARRIER handling on request > queue is not sufficient for sequencing and ordering of requests and why > xen-blkfront and qemu have to do something about it. > > I am also wondering if virtio-blk have similar issues? Mainline xen-blkfront was using ORDERED_TAG before, which meant bypassing the sequencer entirely, as well as not beeing able to implement plain cache flushes as used by ->fsync.